Photopolymerization is a process which leads to the formation of a polymer from monomeric molecules. Many photopolymerizable materials are known in the art, and have been used to form resist and other types of images.
A good review of photopolymerization processes appears in Chapter X of Imaging Systems, Jacobson and Jacobson, John Wiley & Sons, N.Y., N.Y., pp. 181-222 (1976). Dye-sensitized photopolymerization systems are discussed in some detail; see, for example, pp. 184, 195-197, and 214-216. A wide variety of ethylenic unsaturated monomers are noted as useful in such systems. The use of methylene blue as a dye sensitizer in combination with sodium p-toluene sulfinate as a polymerization initiator is noted as a particularly useful photopolymerization initiation system with barium diacrylate and acrylamide, and such a photopolymerizable composition also is noted as useful as a holographic recording material. U.S. Pat. No. 3,694,218 issued to Margerum et al on Sept. 26, 1972 describes the formation of holograms using a similar photopolymerization system comprising, e.g., barium diacrylate, lead diacrylate, acrylamide, methylene blue, p-toluenesulfinic acid sodium salt and 4-nitrophenylacetic acid sodium salt.
Photopolymerization systems of the type described in the aforementioned Margerum, et al. patent are liquids, and are used by being placed between glass slides spaced apart to form a thin cell. The addition of a film-forming thickener to increase viscosity or to form a film has been proposed in U.S. Pat. No. 3,594,204 issued Aug. 3, 1971 to Rust; examples of proposed polymeric thickeners include gelatin, polyvinyl alcohol, polyvinylpyrrolidone and cellulosic compounds. A similar disclosure appears in U.S. Pat. No. 3,531,281 issued Sept. 29, 1970 to Rust, wherein the addition of polyvinyl pyrrolidone is said to be for the purpose of adding viscosity to the solution so that it would form a more satisfactory film on glass.
Margerum et al have reported on a number of "catalysts" or polymerization initiators used in combination with methylene blue and acrylamide in a paper "Studies on the Mechanism of Dye-sensitized Photopolymerization Initiation", Polymer Preprints for the 160th American Chemical Socity Meeting, Chicago, Ill. Sept. 15, 1970, pp. 634-644. In some instances, a mixture of acrylamide and barium diacrylate was used. Margerum et al concluded that the sulfinate ions were far superior to such other catalysts as triethanolamine and ethylenediamine tetraacetic acid (EDTA). Sugawara et al (Applied Optics, Vol. 14, February 1975; pp. 378-382) have reported on the use of acetylacetone and triethanolamine as initiators with acrylamide and methylene blue.
U.S. Pat. No. 4,173,474 issued Nov. 6, 1979 in the name of Tanaka et al. discloses the formation of holograms by the photopolymerization of a monomer, e.g., barium acrylate, in a carrier polymer, e.g., gelatin, followed by immersion in one or more solvents such as isopropanol. Tanaka et al mention polyethylenimine and polyvinyl pyrrolidone in a long list of alternative polymers suitable for use as the carrier polymer; note col. 3, line 67 to col. 4, line 19. The carrier polymer is selected on the basis of its swellability when contacted by a solvent after photopolymerization; see col. 2, lines 23-25.
U.S. Pat. No. 3,445,229 issued May 20, 1969 in the name of Webers discloses a photopolymerizable composition designed to result in exposed areas becoming resistant to thermal softening so that only unexposed areas will transfer when the exposed layer is heated and pressed against a receiving sheet. Webers was concerned with preventing background stain due to transfer from the exposed areas of the acid dye used to color the image. His solution was to immobilize the acid dye using the acid salt of a basic nitrogen compound. A number of basic nitrogen compounds are disclosed as useful in their acid salt forms, including polyethylenimine, e.g., polyethylenimine acetate.
British Pat. No. 924,238 discloses photopolymerization systems in which ethylenically unsaturated compounds are photopolymerized in the presence of a reducing compound in combination with a sensitizing dye chemically linked via an amide group to a polyamine, e.g., polyvinylamine or polyethylenimine.
None of the above-noted references disclose or suggest the use of linear polyethylenimine and a dye sensitizer to initiate photopolymerization.
The copending application of Herbert J. Fielding and Richard T. Ingwall, Ser. No. 641,993 filed Aug. 20, 1984 (now U.S. Pat. No. 4,588,664 issued May 13, 1986) discloses and claims the use of branched polyethylenimine as a photopolymerization initiator in dye sensitized photopolymerizations. A comparison is made in that application between linear and branched polyethylenimine as a photopolymerization initiator, and it was concluded that "linear polyethylenimine is considered to be ineffective as a photopolymerization initiator".